Oxidative dehydrogenation of olefins to diolefins

ABSTRACT

There is disclosed a method comprising the oxidative dehydrogenation of at least one hydrocarbon selected from the group consisting of butene-1, butene-2, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, n-pentene, 2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene, 2-methyl-1-pentene, 2-methyl-2-pentene, 4-methyl-2-pentene, 3-methyl-1-pentene, 3-methyl-2-pentene, 2-ethyl-1-butene, ethyl benzene and isopropyl benzene at oxidative dehydrogenation conditions while in contact with a catalyst consisting essentially of a mixture of cobalt and molybdenum in combination with oxygen which is activated with chromium in combination with oxygen, said catalyst being calcined for at least 1 hour at 400° C. to 1100° C. prior to use.

This application is a continuation-in-part of application Ser. No.614,383, filed Sept. 18, 1975, now abandoned.

This application is directed to a process of the oxidativedehydrogenation of hydrocarbons.

For instance, employing the process of this invention, butene-1 and/orbutene-2 can be oxidatively dehydrogenated to butadiene, isoamylenessuch as 2-methyl-1-butene, 2-methyl-2-butene and 3-methyl-1-butene toisoprene, n-pentenes to piperylene, 2,3-dimethyl-1- or 2-butenes to2,3-dimethyl-1,3-butadiene, methyl pentenes such as 2-methyl-1-pentene,2-methyl-2-pentene, 4-methyl-2-pentene, 3-methyl-1-pentene,3-methyl-2-pentene and 2-ethyl-1-butene to methyl pentadienes, ethylbenzene to styrene and isopropyl benzene to α-methyl styrene.

The invention provides an oxidative dehydrogenation process whichreduces or eliminates endothermic heat requirements, permits continuousburn-off of carbon from the catalyst, permits longer catalyst life,provides higher per pass conversions and higher yields or selectivity tothe desired products. The process also allows the direct efficientconversion of 1-olefins to diolefins, usually only 2-olefins are readilyconverted to diolefins. Thus, the process of this invention is somewhatof an improvement over those of the prior art.

According to the invention, hydrocarbons are oxidatively dehydrogenatedby subjecting at least one hydrocarbon selected from the groupconsisting of butene-1, butene-2, 2-methyl-1-butene, 2-methyl-2-butene,3-methyl-1-butene, n-pentene, 2,3-dimethyl-1-butene,2,3-dimethyl-2-butene, 2-methyl-1-pentene, 2-methyl-2-pentene,4-methyl-2-pentene, 3-methyl-1-pentene, 3-methyl-2-pentene,2-ethyl-1-butene, ethylbenzene and isopropyl benzene to oxidativedehydrogenation conditions while in the presence of a catalystcomprising a mixture of cobalt and molybdenum in combination with oxygenand/or zinc and molybdenum in combination with oxygen which is activatedwith chromium in combination with oxygen, said catalyst being calcinedfor at least one hour at 400° C to 1100° C prior to use.

It has been discovered that if the catalyst mixture is treated with amodifier such as an alkali metal oxide or hydroxide or an alkaline earthoxide or hydroxide in amounts so that the modifier shall range from 0.1to 5 weight percent calculated as the oxide of the alkali or alkalineearth metal based on the weight of the other catalyst components priorto its being finally calcined, the activity of the catalyst is enhancedsomewhat.

The catalyst of this invention can be employed with good success withoutthe use of a support. However, it is believed that the catalyst of thisinvention is best employed by impregnating the mixture of catalystcomponents on a support. Examples of such useful support materials arealumina, silica-alumina, silicon, silicon carbide, pumice and the like.Of these, it is preferred to utilize alumina as the support material.When a support is employed for the catalyst, the amounts of catalystcomponents impregnated on the support should range from about 1 to about25 weight percent, with from about 15 to about 20 weight percent beingmore preferred, calculated as cobalt molybdate and/or zinc molybdate.The amount of chromium impregnated should range from about 1.5 to about40 weight percent calculated as chromium trioxide, with 12 to about 27weight percent being more preferred.

The relationship of the chromium calculated as chromium trioxide to thecobalt and molybdenum and/or zinc and molybdenum employed may beexpressed as the ratio of the atomic weight of chromium to the atomicweight of the total of the cobalt and molybdenum and/or zinc molybdenum(Cr/CoMo or Cr/ZnMo). Thus, the Cr/CoMo or Cr/ZnMo should range from0.1/1 to 5/1 with from 0.25/1 to 4/1 being more preferred and 0.5/1 to3/1 being most preferred. On the other hand, good results have beenobtained when the loadings on the support are approximately equal weightratios of the chromium as chromium trioxide to the cobalt, zinc andmolybdenum calculated as CoMoO₄ or ZnMoO₄.

The catalyst of the invention can be prepared by conventionaltechniques. The preferred techniques are to use the available CoMoO₄ andZnMoO₄. To prepare the catalyst, one needs only to dissolve the cobaltor zinc molybdate in a slightly acidified water solution, for instance,15-20 percent by weight HCl, and impregnate the desired support withsufficient amounts of such solution to impart the desired residualamount calculated as CoMoO₄ or ZnMoO₄, dry this mixture. Then dissolvethe water soluble chromium trioxide, CrO₃, also commercially available,and impregnate the support with sufficient CrO₃ to give the desiredamount of chromium calculated as CrO₃. These impregnations can beconducted in any order. It has been found that either catalyst componentcan be impregnated onto the support and dried or calcined betweenimpregnations. On the other hand, the catalysts of the invention may beprepared by other techniques using the salts of cobalt, zinc, molybdenumand chromium in the proper amounts to give the desired amounts in thefinished catalysts. Representative of these salts are nitrates, halides,oxyhalides and oxalates. The oxides of these metals may also be used insome cases. These techniques are known to those skilled in the art.

If it is desired to use alkali metal or alkaline earth metal oxides, aconvenient method is to utilize a water solution of the hydroxide andimpregnate the support with a sufficient amount to give the desiredamount of alkali metal or alkaline earth metal oxide after calcining.After the catalyst components have been impregnated on the support, thecatalyst may be allowed to dry and is calcined or calcined wet for atleast 1 hour or more at temperatures ranging from about 400° to about600° C.

It has been discovered however that the activity of the catalyst isgreatly enhanced if there is an additional calcining treatment attemperatures between about 750° C and 1100° C for at least 1 hour priorto use as an oxidative dehydrogenation catalyst. There seems to be noupper limit as to the time which the catalyst can be calcined.Successful catalysts have been prepared which were calcined as long as72 hours.

All of the foregoing is not to say that the catalyst cannot be employedwithout the use of a support.

It is usually conventional in a heterogeneous catalyst process such asthat of this invention to employ continuous reaction systems eitherusing fixed beds or fluidized beds. Therefore, it is usually preferredto employ the catalysts of this invention in a form which will not crushor become pulverized readily. For that reason, it is usually moresatisfactory to impregnate the catalyst onto a suitable rugged support,such as those mentioned previously.

The oxidative dehydrogenation process of this invention can be conductedunder fairly reasonable reaction conditions. For instance, thetemperatures employed may vary from about 350° C to 650° C with 450° Cto 575° C being more preferred.

In order to provide a better temperature control of the process, it isusually desirable to employ a diluent, but a diluent is not absolutelyrequired. Materials such as steam, nitrogen, methane, hydrogen, carbondioxide or other diluents known to be stable under the reactionconditions may be employed. Steam is preferred. When a diluent isemployed, the diluent to hydrocarbon mole ratio may be from 1/1 to 20/1with a more preferred range of 2/1 to 5/1.

While oxygen may be used as an oxidant, it is more economical andusually preferred to employ air as the oxidant. The oxidant mole ratioto the hydrocarbon feed in terms of O₂ /HC should be between 0.1/1 and10/1 with a more preferred range being 0.5/1 to 5/1.

The rate at which the hydrocarbon is passed through the reactor and isin contact with the catalyst is the Liquid Hour Space Velocity (LHSV)and is defined as the volume of hydrocarbon as a liquid passed over agiven volume of catalyst per hour. The LHSV employed in this inventionshould range from about 0.1 to about 100 with a more preferred LHSV of0.5 to 10 being employed.

One particularly interesting embodiment of this process is thepreparation of 2,3-dimethyl-1,3-butadiene by the oxidativedehydrogenation of 2,3-dimethyl-2-butene and/or 2,3-dimethyl-1-butene,particularly mixtures where the 2-olefin is in the range of from about65 to 80 mole percent.

The invention is further illustrated by reference to the followingexamples which are intended to be representative rather than restrictiveof the scope.

In the examples, a stainless steel tube of 0.43" internal diameter wasused as a reactor. In this reactor there was placed 6 cubic centimeters(cc) of the particular catalyst employed. The reactor was heated in atubular furnace and temperature controlled by means of thermocouplesplaced at various locations. The hydrocarbon feed and the water diluentwere introduced as liquids using syringe infusion pumps. The air, usedas an oxidant, was metered into the system. The reactor effluent wasanalyzed using gas chromatographic techniques. All percentages arereported by weight except as noted.

EXAMPLE I

In this experiment, run 1 is considered to be a control and the catalystwas prepared by impregnating 30 grams of alumina (8 to 16 mesh which hadbeen dried at 900° C with 0.3 g of KOH dissolved in 15 cc of water)followed by calcination for 1 hour at 520° C. Then 4.5 grams of CoMoO₄dissolved in 15 cc of 18 weight percent HCl was added to the alumina andcalcined for 1 hour at 400° C. Prior to use, the catalyst was calcinedfor approximately 1 hour at 940° C. The catalyst thus calculates to be15 weight percent CoMoO₄ plus 0.5 weight percent K₂ O.

The catalyst employed in run 2 was prepared by impregnating 10 grams ofa commercial catalyst containing 19 percent Cr₂ O₃ on alumina which hadbeen calcined for approximately 1 hour at 600° C with 0.1 gram of KOHdissolved in 5 cc of water followed by calcination at 600° C forapproximately 1 hour, then 1.5 grams of CoMoO₄ dissolved in 18 weightpercent HCl solution was added to this mixture followed by calcining at600° C for approximately 1 hour. Prior to use, the catalyst was calcinedfor approximately 1 hour at 940° C. The finished catalyst calculates tobe 19 percent Cr₂ O₃ plus 0.5 K₂ O plus 15 percent CoMoO₄ on alumina,all percentages in weight percent. Run 2 is considered representative ofthe invention. 2,3-Dimethyl-2-butene was used as the feed at an LHSV of0.5 to 525° C. The results and some operating conditions are given inTable 1 below. Col 1 is the run number, Col 2 is the conversion of the2,3-dimethyl-2-butene (DMB2) in mole percent, Col 3 is the selectivityto 2,3-dimethylbutadiene (DMBD), Col 4 is the mole ratio of water (usedas a diluent) to the hydrocarbon feed, Col 5 is the ratio of air tohydrocarbon feed calculated as the mole ratio of oxygen to DMB2.

                  TABLE 1                                                         ______________________________________                                        1          2        3        4       5                                        ______________________________________                                        Run 1      64       82       4.0     1.3                                      Run 2      76       81       3.2     1.3                                      ______________________________________                                    

EXAMPLE II

In this experiment, run 1 is considered a control and run 2 isconsidered representative of the invention. In these experiments, thecatalysts were prepared as in Example I. The difference between ExampleI and Example II is that 2,3-dimethyl-1-butene (DMB1) was employed asthe olefin to be oxydehydrogenated instead of 2,3-dimethyl-2-butene. InTable 2, Col 1 is the olefin oxydehydrogenated, Col 2 is the conversionof the DMB1 in mole percent, COL 3 is the selectivity to thecorresponding diolefin, DMBD, in mole percent, Col 4 is the mole ratioof the diluent, (H₂ O or steam), to the feed, Col 5 is the mole ratio ofthe oxidant to feed (air), calculated as mole ratio of O₂ to feed.

                  TABLE 2                                                         ______________________________________                                        1          2        3        4       5                                        ______________________________________                                        DMB1       50       68       3.7     1.4                                      DMB1       64       76       3.0     1.3                                      ______________________________________                                    

EXAMPLE III

In these experiments, run 1 is considered to be a control and thecatalyst there employed was prepared by drying 10 grams of Al₂ O₃ at400° C and impregnating this alumina with 0.1 gram of KOH dissolved in 5cc water followed by calcining at 400° C for 1 hour. Then 1.5 gramsCoMoO₄ dissolved in 5 cc of 18 weight percent HCl was added and calcinedat 918° C for approximately 1 hour.

The catalyst employed in run 2 which represents the practice of theinvention was prepared by drying 100 grams of a commercial catalystconsisting of 19 weight percent Cr₂ O₃ on alumina at 600° C followed by1 gram of KOH dissolved in 25 cc water and calcining at 600° C forapproximately 1 hour. Then 15 grams of CoMoO₄ dissolved in 25 cc of 18weight percent HCl solution was added and dried at 600° C. The catalystreceived a final calcining at 940° C for approximately 1 hour prior touse.

In these runs, 2-methyl-2-butene (2MB2) was employed as the olefinoxydehydrogenated at an LHSV of 0.5 and the temperature was maintainedat 525° C. In Table 3, Col 1 is the olefin, Col 2 is the conversion ofthe olefin in mole percent, Col 3 is the selectivity to thecorresponding diolefin, isoprene, in mole percent, Col 4 is the moleratio of the diluent (water) to the feed, Col 5 is the mole ratio of theoxidant (air) to the feed calculated as the mole ratio of O₂.

                  TABLE 3                                                         ______________________________________                                        1          2        3        4       5                                        ______________________________________                                        2MB2       29       45       3.0     1.0                                      2MB2       19       69       2.3     1.0                                      ______________________________________                                    

EXAMPLE IV

In this example, all the runs were conducted with a feed which was2,3-dimethyl-2-butene at an LHSV of 0.5 at two different temperatureswhich are listed in Table 4. In run 1, the catalyst employed was 19weight percent Cr₂ O₃ on alumina which had been calcined at 950° C., andis a control. Run 2 catalyst was prepared by impregnating 10 grams ofalumina with 1.5 grams of CoMoO₄ dissolved in 5 cc of 18 weight percentHCl solution which was calcined at 940° C for 1 hour, and is a control.Run 3 the catalyst was prepared by impregnating 20 grams of a commercialcatalyst which was 19 percent Cr₂ O₃ on alumina with 3 grams of CoMoO₄and calcining the catalyst at 625° C for approximately 1 hour. Thecatalyst received a final calcination prior to use at 960° C forapproximately 1 hour, thus is representative of the invention. Run 4 thecatalyst was the same as the catalyst in run 2 except it contained 0.5weight percent K₂ O, and is a control. In run 5 the catalyst wasprepared by impregnating 10 grams of 19 weight percent Cr₂ O₃ on aluminawith 0.1 gram of KOH in 2.5 cc of water calcined at 600° for 1 hour,then 1.5 gram CoMoO₄ in 2.5 cc 18 percent HCl solution was added. Thecatalyst was calcined for 1 hour at 600° C. The catalyst received afinal calcination at 940° C for 1 hour. Thus, runs 1, 2 and 4 areconsidered controls and runs 3 and 5 represent the invention. In run 6the catalyst was prepared 20 grams of 19 percent by weight Cr₂ O₃ onalumina with 3 grams of CoMoO₄ and calcining the catalyst for 1 hour at625° C. The catalyst received a final calcining at 960° forapproximately 1 hour prior to use. The catalyst employed in run 7 isidentical to that of run 6 except that it contained 0.1 weight percentK₂ O and the catalyst received a final calcining of 800° C for a periodof 16 hours. In run 8 the catalyst employed was approximately the sameas that employed in run 6 except it contained 0.5 weight percent K₂ O.Thus runs 6 and 8 represent the invention. In Table 4, the results andsome operating conditions are given. Col 1 is run number, Col 2 istemperature, Col 3 is the conversion of the 2,3-dimethyl-2-butene inmole percent, Col 4 is the selectivity to 2,3-dimethylbutadiene in molepercent, Col 5 is the mole ratio of the water to feed and Col 6 is themole ratio of air to feed calculated as O₂.

                  TABLE 4                                                         ______________________________________                                        1       2        3       4     5      6                                       ______________________________________                                        1       525      37      56    3.3    1.2                                     2       525      59      74    3.3    1.2                                     3       525      75      72    2.9    1.6                                     4       525      57      72    3.2    1.2                                     5       525      64      76    3.0    1.3                                     6       450      75      79    3.2    1.3                                     7       450      42      71    4.0    1.7                                     8       450      49      86    2.9    1.4                                     ______________________________________                                    

EXAMPLE V

In these experiments 2,3-dimethyl-2-butene was oxidativelydehydrogenated with the same catalyst at several different temperaturesat an LHSV of 0.5. The catalyst employed was prepared by impregnating0.1 gram of KOH onto 10 grams of 19 weight percent Cr₂ O₃ on alumina andheating to 600° C for approximately 1 hour. Then 1.5 grams of CoMoO₄ wasimpregnated onto the catalyst and heated for 1 hour at 600° C. Thecatalyst received a final calcining of 940° C. for 1 hour prior to use.The results and some operating conditions are reported in Table 5, inwhich Col 1 identifies the catalysts, Col 2 the temperature in ° C, Col3 the conversion of DMB2 in mole percent, Col 4 the selectivity to DMBDin mole percent, Col 5 the mole ratio steam to DMB2 and Col 6 the O₂ toDMB2 mole ratio.

                  TABLE 5                                                         ______________________________________                                        1       2        3       4     5      6                                       ______________________________________                                        A       525      64      76    3.0    1.3                                     A       500      64      80    3.2    1.3                                     A       475      50      83    3.0    1.2                                     A       450      36      91    3.1    1.3                                     ______________________________________                                    

EXAMPLE VI

This example illustrates the use of a non-supported catalyst. Thecatalyst employed in run 1 was 10 grams of CoMoO₄ to which was added 3.2grams of CrO₃ in 5 cc of water and calcined at 640° C. The catalystemployed in run 2 was identical to run 1 except that it was recalcinedat 940° C for approximately 1 hour just prior to use.2,3-dimethyl-2-butene was dehydrogenated at an LHSV of 0.5 at 450° C.Col 1 is the mole percent conversion of the 2-methyl-butene-2, Col 2 isthe selectivity to 2,3-dimethyl butadiene, Col 3 is the water tohydrocarbon ratio and Col 4 is the O₂ to hydrocarbon ratio employed.

                  TABLE 6                                                         ______________________________________                                        1           2         3          4                                            ______________________________________                                        76          78        3.7        1.7                                          79          80        4.1        2.1                                          ______________________________________                                    

EXAMPLE VII

In this example, all runs were made using 2,3-dimethyl-2-butene as thefeed at an LHSV of 0.5. In runs 2 and 3, the catalyst was prepared bydrying 10 grams of Al₂ O₃, impregnating 3.2 grams of CrO₃ dissolved in 5cc of water, followed by calcining at 640° C, then 0.1 gram of KOHdissolved in 5 cc water was added followed by calcining at 640° C, then1 gram of ZnMoO₄ dissolved in 5 cc of 18 weight percent HCl was added,followed by calcining at 640° C. The two additions of ZnMoO₄ was madebecause of the solubility problem with ZnMoO₄. The catalyst received afinal calcination at 980° C for 1 hour prior to use.

The catalyst employed in runs 2 and 4 were prepared in the same natureas the catalyst of runs 1 and 3 except that the final addition of ZnMoO₄was 1.5 gram instead of 1.0 gram.

The results and operating conditions are given in Table 7 below in whichCol 1 is the run number, Col 2 is the oxidative dehydrogenationtemperature, Col 3 is the conversion of DMB2, Col 4 is the selectivityto DMBD, Col 5 is the H₂ O/HC mole ratio, Col 6 is the O₂ /HC moleratio.

                  TABLE 7                                                         ______________________________________                                        1      2         3       4     5       6                                      ______________________________________                                        1      525       81      77    3.4     1.6                                    2      525       80      77    4.4     1.5                                    3      450       61      83    3.9     1.8                                    4      450       71      82    4.1     1.8                                    ______________________________________                                    

Thus, the examples set forth above indicate an improvement in the chromemodification of catalysts comprising zinc molybdate and cobaltmolybdate, and optionally some alkali metal oxides may also be included.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A process of oxidative dehydrogenation whichcomprises subjecting at least one hydrocarbon from the group ofbutene-1, butene-2, 2-methyl-1-butene, 2-methyl-2-butene,3-methyl-1-butene, n-pentene, 2,3-dimethyl-1-butene,2,3-dimethyl-2-butene, 2-methyl-1-pentene, 2-methyl-2-pentene,4-methyl-2-pentene, 3-methyl-1-pentene, 3-methyl-2-pentene and3-ethyl-1-butene to oxidative dehydrogenation conditions while saidhydrocarbons are in the presence of a catalyst consisting essentially ofa mixture of cobalt molybdate (CoMoO₄) and at least one of chromiumoxide (CrO₃ or Cr₂ O₃), said catalyst mixture being calcined for atleast one hour at 400° to 1100° C. prior to use, in which therelationship of the chromium to cobalt and molybdenum expressed as theatomic ratio of chromium (Cr) to the total of the cobalt and molybdenum(CoMo) ranges from about 0.1/1 to about 5/1.
 2. The process according toclaim 1 in which the catalyst is impregnated on a support.
 3. Theprocess according to claim 2 in which the amount of catalyst impregnatedon the support ranges from about 1.5 to about 40 weight percent ofchromium calculated as CrO₃ and the amount of cobalt and molybdenumcalculated as cobalt molybdate ranges from about 1 to about 25 weightpercent.
 4. The process according to claim 3 in which the support isalumina.
 5. The process according to claim 1 in which water is employedas a diluent.
 6. The process according to claim 1 in which thehydrocarbon is selected from the group of 2,3-dimethyl-1-butene and/or2,3-dimethyl-2-butene.
 7. The process according to claim 1 in which airis employed as an oxidant in amounts to provide an oxygen/hydrocarbonmole ratio of 0.5/1 to 5/1.
 8. The process according to claim 1 in whichthe air is employed as an oxidant in amounts to provide anoxygen/hydrocarbon mole ratio of 0.5/1 to 5/1 and in which the catalystis impregnated on an alumina support in amounts ranging from about 12 toabout 27 weight percent by weight of CrO₃ and from about 15 to about 20weight percent of CoMoO₄ by weight of alumina as the support and inwhich water is employed as a diluent in amounts to give a mole ratio ofdiluent/hydrocarbon of about 2/1 to about 5/1.
 9. The process accordingto claim 8 in which the hydrocarbon is 2,3-dimethyl-1-butene and/or2,3-dimethyl-2-butene.
 10. The process according to claim 1 in which thecatalyst is treated with a modifier comprising an alkali metal oxide orhydroxide or an alkaline earth metal oxide or hydroxide in amountsranging from 0.1 to 5 weight percent based on the weight of the othercatalyst components.